For optimal care of betta fish, a 20–40 cm cubic tank is recommended for single-fish keeping. The exact size can be adjusted based on your care needs and available space. Below is a detailed breakdown:
I. Basic Size Requirements
Minimum Sizes
Betta fish are fast swimmers with strong territorial instincts, requiring ample space to move freely.
10 cm cubic or round tanks: Too small, increasing the risk of bettas hitting the tank walls, poor water quality regulation, and oxygen depletion-induced jumping. Not recommended.
15 cm cubic tanks: Suitable as temporary housing for single bettas. Daily 25% water changes and strict temperature control (25–28°C) are mandatory; long-term use may raise maintenance difficulty.
20 cm cubic tanks: Ideal for single bettas, offering stable water conditions. Water changes can be reduced to 1–2 times weekly, making it perfect for beginners.
Recommended Sizes
20–40 cm cubic tanks: Provide sufficient swimming space and stable water quality, minimizing frequent water change hassle.
30 cm cubic tanks: Compatible with sponge filters or small hang-on-back filters, further reducing water parameter fluctuations—ideal for long-term care.
Tanks over 40 cm: Suitable for community keeping (with dividers) or aquascaping with live plants and driftwood to mimic a natural ecosystem.
II. Core Principles for Size Selection
Space Needs
Though small (5–7 cm adult length), bettas require extensive swimming room to avoid stress-related issues like depression or fin rot.
Cubic tanks are preferred over round or irregularly shaped ones, as the latter can disorient bettas.
Water Quality Management
Larger tanks maintain more stable water conditions, with lower concentrations of harmful substances like ammonia and nitrite.
Small tanks (e.g., 15 cm): Require daily water changes.
Medium/large tanks (e.g., 30 cm): Only need 25–50% water changes weekly, reducing maintenance frequency.
Filter Compatibility
Tanks under 20 cm: Use small sponge or hang-on-back filters to avoid strong water flow.
Tanks over 30 cm: Low-flow filters are recommended to keep water clear without disturbing bettas.
III. Size Recommendations for Special Scenarios
Breeding Period
Prepare a separate 15 cm cubic breeding tank with floating plants or a bubble nest, facilitating nest-building and spawning.
Community Keeping
For multiple bettas, use a large divided tank or modular aquarium. Allocate at least 20 cm of space per fish to prevent aggression.
Temporary/Portable Housing
A 15 cm cubic tank works for short-term transport or observation, but requires enhanced water quality monitoring and frequent changes.